Charmonium production in p – A collisions is a unique tool for the study of the interaction of bound c c states in nuclear matter. It can provide details on the basic features of the resonance formation mechanism and, in particular, on its non-perturbative aspects. In this Letter, we present an experimental study of charmonia and Drell–Yan production in proton–nucleus collisions at 450 GeV/ c . The results are analyzed in the framework of the Glauber model and lead to the values of the nuclear absorption cross-section σ abs pA for J / ψ and ψ ′. Then, we compare the J / ψ absorption in proton–nucleus and sulphur–uranium interactions, using NA38 data. We obtain that, for the J / ψ , σ abs pA and σ abs SU are compatible, showing that no sizeable additional suppression mechanism is present in S–U collisions, and confirming that the anomalous J / ψ suppression only sets in for Pb–Pb interactions.
The J/PSI production cross section times the branching ratio to MU+ MU- pernucleon-nucleon collision for the differential nuclear targets.
The PSI(3685) production cross section times the branching ratio to MU+ MU-per nucleon-nucleon collision for the differential nuclear targets.
The Drell Yan cross section, divided by the mass number A, and multiplied by the isospin correction factors in the mass interval 2.9 to 4.5 GeV.
A partial-wave analysis has been performed of the diffractively produced low-mass ( K ̄ 0 π − π 0 ) system in the reaction K − p → ( K ̄ 0 π − π 0 ) p at 10 and 16 GeV/ c . Thus information complementary to that derived from the K − p → (K − π + π − )p) channel is obtained. The presence of the K ϱ decay mode, besides the dominant K ∗ (890)π mode, for the state J P = 1 + , is confirmed. It is also confirmed that for this 1 + state the assumption of factorization of the amplitude into “production” and “decay” does not hold: the two decay modes K ∗ π and K ϱ have different polarisation properties (helicity is approximately conserved in the t -channel for the first, in the s -channel for the second). The assumption that the ( K ̄ 0 π − π 0 ) system has isospin I = 1 2 has been tested and found to hold. From the cross sections for the various J P states, assuming I = 1 2 , the cross sections for the (K − π + π − ) system are predicted and compared with the experimental ones. In general, agreement is found.
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We report a measurement of the exclusive \$e^+e^- \to \Lambda_c^+ \Lambda_c^-$ cross section as a function of center-of-mass energy near the $\Lambda_c^+ \Lambda_c^-$ threshold. A clear peak with a significance of $8.8\sigma$ is observed in the $\Lambda_c^+ \Lambda_c^-$ invariant mass distribution just above threshold. With an assumption of a resonance origin for the observed peak, a mass and width of $M=(4634^{+8}_{-7} \mathrm{(stat.)} ^{+5}_{-8} \mathrm{(sys.)})\mevc$ and $\Gamma_{\mathrm{tot}}=(92^{+40}_{-24} \mathrm{(stat.)}^{+10}_{-21} \mathrm{(sys.)})\mev$ are determined. The analysis is based on a study of events with initial-state-radiation photons in a data sample collected with the Belle detector at the $\Upsilon(4S)$ resonance and nearby continuum with an integrated luminosity of 695 $\mathrm{fb}^{-1}$ at the KEKB asymmetric-energy $e^+e^_$ collider.
Cross section for the exclusive process E+ E- --> LAMBDA/C+ LAMBDA/CBAR-.
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Electron-proton elastic-scattering cross sections have been measured at the Stanford Linear Accelerator Center for four-momentum transfers squared q 2 from 1.0 to 25.0 (GeVc)2. The electric (GEp) and magnetic (GMp) form factors of the proton were not separated, since angular distributions were not measured at each q 2. However, values for GMp were derived assuming various relations between GEp and GMp. Several theoretical models for the behavior of the proton magnetic form factor at high values of q 2 are compared with the data.
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We have measured the total inelastic cross section (σinel) and charged-particle multiplicities obtained in pp collisions at 405 GeV/c. The data are from a preliminary 12 000-picture bubble-chamber exposure. We find σinel=32.8±1.0 mb; the low moments of the multiplicity distribution for negative particles are 〈n−〉=3.50±0.07, D−=2.37±0.05, f2−=2.1±0.2, and f3−=0.1±0.9. We also present updated results at 102 GeV/c.
SUPERCEDES PRELIMINARY RESULTS IN J. W. CHAPMAN ET AL., PRL 29, 1686 (1972).
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FIT TO ELASTIC DIFFERENTIAL CROSS SECTION FOR 0.05 < -T < 0.7 GEV**2.
The first direct measurements of neutron-proton and neutron-deuteron total cross sections in the momentum range 14 to 27 GeV/c are presented. The np total cross section apparently becomes less than the pp total cross section in this momentum region. Our results show no evidence for a rapid vanishing of the Glauber screening correction as predicted by Abers et al. on the basis of Regge theory.
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The reactions π+p→Σ+(1385)K+ and π+p→Σ+(1385)K*+(890) are examined. The Σ+(1385)K+ differential cross section for −t′<0.5 GeV2 and spin density matrix elements agree with a Regge-pole model incorporating (nondegenerate) vector and tensor K* exchange with dominant M1 coupling. The Σ+(1385)K*+(890) density matrix elements are consistent with the quark-additivity predictions. A Y*+ at a mass of 1700 MeV is also observed in the Λπ+ mass distribution, produced opposite both K+ and K*+(890).
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GOTTFRIED-JACKSON FRAME.
The differential cross section for neutron-proton elastic scattering was measured in the diffraction region with incident-neutron momenta between 8 and 30 GeV/c. The experiment was a spark-chamber-counter experiment, conducted at the alternating-gradient synchrotron. Results are presented and compared with currently available lower energy np data and comparable energy pp data.
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We present improved measurements of the differential production rates of stable charged particles in hadronic Z0 decays, and of charged pions, kaons and protons identified over a wide momentum range using the SLD Cherenkov Ring Imaging Detector. In addition to flavor-inclusive Z0 decays, measurements are made for Z0 decays into light (u, d, s), c and b primary flavors, selected using the upgraded Vertex Detector. Large differences between the flavors are observed that are qualitatively consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results are used to test the predictions of QCD in the Modified Leading Logarithm Approximation, with the ansatz of Local Parton-Hadron Duality, and the predictions of three models of the hadronization process. The light-flavor results provide improved tests of these predictions, as they do not include the contribution of heavy-hadron production and decay; the heavy-flavor results provide complementary model tests. In addition we have compared hadron and antihadron production in light quark (as opposed to antiquark) jets. Differences are observed at high momentum for all three charged hadron species, providing direct probes of leading particle effects, and stringent constraints on models.
Production rates of all stable charged particles. The statistical and systematic errors are shown separately for the momentum distribution. They are combined in quadrature for the other two distributions. The first DSYS error is due tothe uncertainty in the track finding efficiency and the second DSYS error is th e rest of the systematic error.
The charged pion fraction and differential production rate per hadronic Z0 decay.
The charged kaon fraction and differential production rate per hadronic Z0 decay.
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